Ceramic dielectrics



sePf- 23, 1969 sl-llNoau FuJlwARA 3,468,680

CERAMIC DIELECTRICS Filed Nov. e, 1967 rl N P1052/ sHlNoBU FUJrwARAATTORNEYS United States Patent Ol 38/ 26,017 Int. Cl. C04b 35/ 00,35/46; H01b 3/12 U.S. Cl. 106--39 7 Claims ABSTRACT F THE DISCLOSURECeramic dielectric materials are provided. Such materials demonstratehigh dielectric constants and small temperature coelicients ofdielectric constants. The dielectric materials are prepared by sinteringat a temperature of about 1350 C. a mixture having the followingcomposition:

Component: Percent by weight SrTiO3 40-80 Bl2o3 MgCO3 5-35 'I'hisapplication is a continuation-in-part application of copendingapplication, Ser. No. 366,732 led May 12, 1964, now abandoned.

The present invention relates to improvements in certain of theproperties of ceramic dielectrics.

The object of the present invention is to provide ceramic dielectricswhich show high dielectric constants and small temperature coeiiicientsof dielectric constants. Therefore, by using the dielectric materials ofthe present invention, small sized capacitors with good temperaturecharacteristics and very small strain inductances can be obtained.

As is well known, ceramics of barium titanate (BaTiO3) are most widelyused for practical purposes. But the applications of a dielectricmaterial of this kind are extremely limited because of the very sharpchange of dielectric constant at the Curie point which lies around 120C. Attempts have been made to smooth out the temperature dependence ofthe dielectric constant. The addition of calcium titanate (CaTiO3) ormagnesium titanate (MgTiOa) smooths out the steep curve depending upontemperature to some extent, but at the same time it involves thelowering of the dielectric constant, which also limits the applicabilityfor practical purposes greatly.

The present invention provides ceramic dielectric with improvedproperties i.e. ceramic dielectrics which show small temperaturecoefcients and good temperature characteristics and at the same timehigh dielectric constants.

A dielectric material of the present invention is produced by sinteringat a temperature of about 1350 C., a mixture having the followingcomposition:

Percent by weight 40-80 Component:

SlTlO3 Bigoa MgCO3 5-35 MnSO, (as a mineralizer) 0.005-1 cient of thedielectric constant becomes too large in negative sign and thetemperature for sintering is required to be higher than l380 C., andwhen it is under 40% by weight, the dielectric constant becomes low andat the same time vitriication becomes diiiicult and the bodies obtainedlose dense structure. When Bi2O3-2TiO2 exceeds 55% Aby weight, thebodies obtained lose dense structure, and when it is under 10%, thetemperature for sintering is required to be higher than 1380 C. When theproportion of magnesium carbonate (MgCO3) exceeds 35% by weight, a highdegree of shrinkage takes place, the dielectric constant becomes toolow, the temperature for sintering is required to be higher than 1400 C.and vitriiication becomes diicult, and when it is under 5% by weight,the temperature coetiicient of the dielectric constant takes a highvalue in negative sign, and so is unsuitable for practical purposes.When the amount of manganese sulfate (MuSO4) is over 1% by weight, theobtained bodies become highly porous :and when it is under `0.005%dielectric loss becomes large.

FIG. 1 is a ternary diagram which shows the relation between dielectricconstant or the temperature coeicient of dielectric constant and theproportions of the three components of the products in accordance withthe present invention, i.e. strontium titanate (SrTiO3), mixture ofbismuth oxide and titanium oxide (Bi2O3-2Ti02) and magnesium carbonateoxide (MgO).

A dielectric material of the present invention is obtained by thefollowing procedure:

After the addition of a suitable mineralizer e.g. manganese sulfate(MnSO4), strontium titanate (SrTiO3) is presintered followed bypowdering, then it is mixed with mixture of bismuth oxide and titaniumoxide.

and magnesium carbonate (MgCO3) and after shaping, the mixture issintered at 1250 C. to 1350 C. in air for 2 to 3 hours.

The sintering temperature and hours of these materials may be varied,deepndent upon the composition. It should not be above the sublimationtemperature.

Some examples of the present invention are given below.

EXAMPLE 1 Manganese sulfate (MnSO4) is added to strontium titanate(SrTiO3) in the proportion of 0.3%, and this material is pre-sintered atl320 C., then powdered and mixed with Bi2O3-2TiO2 and magnesiumcarbonate (MgCOa) in the weight proportion of (SrTiO3) (Bi2O32TiO2)(MgCO3) =57:36:7

and after shaping, the mixture is sintered at 1350 C.

The ceramic dielectrics thus obtained show the following properties:

Dielectric constant 1180 Temperature coeicient of dielectric constant-1100 10/ C.

The properties were measured at 1 mc./s. in this example and also inthefollowing herein.

EXAMPLE 2 After adding 0.3% of manganese sulfate (MnSOi), strontiumtitanate (SrTiO3) is pre-sintered at l320 C. followed by powdering, thenit is mixed with Bi2O3'2TiO2 and magnesium carbonate (MgCO3) in theWeight proportion of SrIiO3zBi2O3-2Ti02:MgCO3=5l:32:17, and the mixtureis shaped and sintered at 1350 C. The properties of the resultantproducts are as follows:

Dielectric constant 945 Temperature coeiiicient of dielectric constanti0 As shown in this example, when the proportion of strontium titanate(SrTiO3) is about 50% by weight, the bodies obtained show excellentproperties. The temperature coeicient of dielectric constant is i and atthe same time, the dielectric constant itself is high enough.

What is claimed is:

1. A ceramic dielectric material sintered from a batch which consistsessentially of 40 to 80% by weight of SrTiO3, to 55% of Bi2O3-2Ti02 and5 to 35% of MgCO3, wherein a small amount of MnSO4 is added as amineralizer to SrTiO3.

2. A ceramic dielectric material sintered from a batch which consistsessentially of 57% by weight of SrTiO3, 36% of Bi2O3-2Ti02 and 7% ofMgCO3, wherein a small amount of MnSO4 is added as a mineralizer toSrTiO3.

3. A ceramic dielectric material sintered from a batch which consistsessentially of 51% by weight of SrTiO3, 32% of Bi2O3-2Ti03 and 17% ofMgCO3, wherein a small amount of MnSO4 is added as a mineralizer toSrTiO3.

4. A ceramic dielectric material as claimed in claim 1, wherein 0.005 to1% by weight of MnSO4 is added as a mineralizer to SrTiO3.

5. A ceramic dielectric material as claimed in claim 2, wherein 0.005 to1% by weight of MnSO4 is added as a mineralizer to SrTiO3.

6. A ceramic dielectric material as claimed in claim 3, wherein 0.005 to1% by weight of MnSO4 is added as a mineralizer to SrTiO3.

7. A method for the preparation of a ceramic dielectric material whichcomprises:

(1) pre-sintering a mixture of SrTiO3 with up to 1% by weight MnSO4 at atemperature of about 1320" C. and powdering the resultant pre-sinteredmaterial;

(2) admixing from 40 to 80% by weight of the powdered pre-sinteredmaterial with 10 to 55% by weight of Bi2O3-2Ti02 and 5 to 35% by weightMgCO3;

(3) forming the mixture to a desired shape; and

(4) sntering the shaped article at a temperature of about 1350 C.

References Cited UNITED STATES PATENTS 5/ 1949 Wainer 106--39 4/ 1965Welsby et al. 106-39 U.S. C1. X.R.

